The present invention relates to image processing and relates to a technology for, for example, decoding compressed image data and performing format-conversion on the decoded data.
Still images and moving images are both configured to be stored/transmitted in compressed states for capacity saving of a medium for storing images and improvement in image transmission speed. In the present specification, when just a word “image” is used, it includes both of the still image and the moving image. In addition, the “image” and “image data” which is data indicating the image are used in the same meaning unless otherwise specifically described.
A device (hereinafter, referred to as an “image utilization device”) on the side that a compressed image is utilized includes a decoder meeting the compression standards (JPEG, MPEG and so forth) of the image and decodes the image by the decoder.
There are cases when an output format of the decoder and a format (hereinafter, referred to as a “utilization format”) that the image utilization device uses for display are different from each other. For example, 3planar is known as an example of an image format (corresponding to the “utilization format”) that Android (a registered trademark) which is OS which is frequently adopted in a smartphone which is one of the image utilization device is allowed to handle as system requirements. On the other hand, 2planar is generally known as an example of the output format of the decoder.
Therefore, it is required to convert the format of image data (decoded data) which has been output from the decoder to the utilization format in the image utilization device.
Technologies which have been made from various viewpoints are proposed for the image utilization device for which both of decoding of the compressed data and format-conversion of the decoded image data are required.
For example, in Japanese Unexamined Patent Publication No. Hei 11 (1999)-275575, there is disclosed a technique for allowing an MPEG decoding device that both of an MPEG decoder for decoding an MPEG image and a format conversion unit for undertaking format-conversion of decoded image data are built in to carry out the format-conversion in both of the exterior and the interior of the MPEG decoding device. The MPEG decoding device to which the above-mentioned technique is applied includes a selector for selectively outputting an output of the MPEG decoder and an output of the format conversion unit. If an external frame memory is coupled to the format conversion unit and the selector prefers to select the output of the format conversion unit, the MPEG encoding device will be allowed to perform processing up to format-conversion. On the other hand, if the selector prefers to select the output of the MPEG decoder and another format conversion unit is installed on the outside of the MPEG decoding device, the MPEG decoding device will be allowed to operate simply as the decoder.
In addition, in Japanese Unexamined Patent Publication No. 2003-169326, there is disclosed a technology that prior to decoding of encoded data (an compressed image), a picture is divided into a plurality of regions per picture and decoding and format-conversion are sequentially and alternately executed again and again in units of divided regions in order to save the capacity of the memory required for decoding and format-conversion. According to this technology, it is allowed to save the memory capacity in comparison with a case that the whole data, that is, one-picture data (data corresponding to one picture) is stored.
Further, in Japanese Unexamined Patent Publication No. Hei 8 (1996)-172602, there is disclosed a technology that in displaying a compressed image, the compressed data is decoded and written into a memory, the decoded data which has been written into the memory is read out by an FIFO in accordance with an output format and is temporarily stored. In this technology, writing of the data from the decoder to the memory is performed in units of blocks and reading of the data from the memory is performed in units of lines by laser scanning for the purpose of capacity saving of the memory for storing the decoded data similarly to the technology described in Japanese Unexamined Patent Publication No. 2003-169326.
The technology disclosed in Japanese Unexamined Patent Publication No. Hei 11 (1999)-275575 is configured such that the decoded data is output from the MPEG decoder directly to the format conversion unit both in a case where the data is format-converted by the format conversion unit built into the MPEG decoding device and in a case where the data is format-converted by the format conversion unit installed on the outside of the MPEG decoding device (see FIGS. 1 to 3 in Japanese Unexamined Patent Publication No. Hei 11 (1999)-275575).
Therefore, there is such a disadvantage that, for example, when processing of format-conversion is delayed, it becomes difficult for the MPEG decoder to transfer the decoded data to the format conversion unit and execution of decoding and/or processing of the entire system delays. This disadvantage will cause to give a user an unpleasant filling, in particular, in case of an image utilization device such as video chat, a wireless display or the like that a reduction in time taken until the compressed data is displayed after it has been input into the decoder is desired.
In the technology disclosed in Japanese Unexamined Patent Publication No. 2003-169326, although it is allowed to perform a process of dividing the picture concerned prior to decoding on a still image of JPEG system or the like in many cases, it is difficult to perform the above-mentioned process on a moving image in many cases. In addition, there is also such a disadvantage that control of picture division and divided-region-based decoding/format-conversion is complicated and a load is imposed on the CPU.
The technology disclosed in Japanese Unexamined Patent Publication No. Hei 8 (1996)-172602 inevitably uses a memory controller (corresponding to a “synchronizing signal generator” in the embodiment of Japanese Unexamined Patent Publication No. Hei 8 (1996)-172602) that generates timings at which addresses in the memory are controlled, the data is written into the memory and the data is read out from the memory. As illustrated in FIG. 3 or the like in Japanese Unexamined Patent Publication No. Hei 8 (1996)-172602, since this synchronizing signal generator generates the timings of data writing, data reading and so forth on the basis of a timing (a horizontal synchronizing signal, a vertical synchronizing signal and so forth) upon data display, control is complicated and the decoder may be kept waiting for the convenience of display. As a result, such a disadvantage occurs that execution of decoding and/or processing of the entire system is delayed.
Other subject matters and novel features of the present invention will become apparent from the description of the present specification and appended drawings.